The accuracy of satellite remote sensing of trace gases by imaging spectrometers depends highly on the uniformity of the instrument spectral response function. Studies have shown that scene inhomogeneity across the spectrometer’s slit width (spectral direction) can cause errors in the measured spectral radiances, leading to trace gas retrieval inaccuracy. One mitigation approach recent imaging spectrometers use is a slit homogenizer to redistribute scene radiance within the slit. This on-board hardware device functions like a slab waveguide, with rays making multiple bounces between narrowly spaced, highly reflective, plane-parallel mirrors. This presents a challenge as any difference in s- and p-polarization reflectance for the mirror surfaces tends to multiply with each bounce, producing a net linear polarization sensitivity (LPS) in the system’s throughput which also results in retrieval error. Our solution is a slit homogenizer design that mitigates for LPS by employing total internal reflection (TIR) and a birefringent internal medium. TIR ensures high and equal reflectance while a birefringent material such as sapphire, with an appropriately oriented optic axis, provides high-order retardance between bounces. This introduces polarization scrambling in the manner of a Lyot-depolarizer. We provide a basic analysis of the device’s geometrical optics, detailing the crystalline optic axis orientation for the device cut from a sapphire boule and readily-available R-cut material. Preliminary lab testing was performed on three mirror-pair and two sapphire plate homogenizers at multiple visible wavelengths. The results show that our sapphire plate slit homogenizers decrease LPS by at least an order of magnitude compared to the mirror-based ones.
The flight of the Micro-X sounding rocket on July 22, 2018, marked the first operation of transition-edge sensors and their superconducting quantum interference device readouts in space. The instrument combines the microcalorimeter array with an imaging mirror to take high-resolution spectra from extended X-ray sources. The first flight target was the Cassiopeia A supernova remnant. Although a rocket pointing malfunction led to no time on-target, data from the flight were used to evaluate the performance of the instrument and demonstrate the flight viability of the payload. The instrument successfully achieved a stable cryogenic environment, executed all flight operations, and observed X-rays from the on-board calibration source. The flight environment did not significantly affect the performance of the detectors compared with ground operation. The flight provided an invaluable test of the impact of external magnetic fields and the instrument configuration on detector performance. This flight provides a milestone in the flight readiness of these detector and readout technologies, both of which have been selected for future X-ray observatories.
This paper summarizes our current instrument prototyping efforts of miniature near-UV imaging spectro-polarimeters to probe the thermodynamics and magnetism of the solar Chromosphere and Transition Region. This includes our high altitude balloon piggyback instruments DIMS-RADIANCE and DIMS-STOUT, which are scheduled to fly in 2018. These payloads are CubeSat sized instruments designed around commercial off-the-shelf miniaturized spectrographs. Additionally we detail a new optical concept and proposed CubeSat mission called SolarCube. This instrument will be capable of “snapshot polarimetry” with simultaneous 2D imaging, spectroscopy, and linear polarization without mechanisms or scanning. This concept utilizes an integral field unit, diffraction grating, and unique polarization sensitive detector. The design, capabilities, current prototyping efforts, and future plans are discussed. The design goal is to observe the spatially resolved polarization signature of the Mg II h-k doublet at 280nm over the full solar disk.
The COronal Solar Magnetism Observatory (COSMO) is a proposed facility with unique capabilities for magnetic field measurements in the solar atmosphere and corona to increase our understanding of solar physics and space weather. The observatory underwent a preliminary design review (PDR) in 2015. This paper summarizes the systems engineering plan for this facility as well as a preliminary overview of the concept of operations. In particular we detail the flow of science requirements to engineering requirements, and discuss an overview of requirements management, documentation management, interface control and overall verification and compliance processes. Operationally, we discuss the categories of operational modes, as well as an overview of a daily operational cycle.
The Coronal Solar Magnetism Observatory Large Coronagraph (COSMO-LC) is a 1.5 meter Lyot coronagraph dedicated to measuring magnetic fields and plasma properties in the solar corona. The COSMO-LC will be able to observe coronal emissions lines from 530-1100 nm using a filtergraph instrument. COSMO-LC will have a 1 degree field of view to observe the full solar corona out to 1 solar radius beyond the limb of the sun. This presented challenges due to the large Etendue of the system. The COSMO-LC spatial resolution is 2 arc-seconds per pixel (4k X 4k). The most critical part of the coronagraph is the objective lens that is exposed to direct sunlight that is five orders of magnitude brighter than the corona. Therefore, it is key to the operation of a coronagraph that the objective lens (O1) scatter as little light as possible, on order a few parts per million. The selection of the material and the polish applied to the O1 are critical in reducing scattered light. In this paper we discuss the design of the COSMO-LC and the detailed design of the O1 and other key parts of the COSMO-LC that keep stray light to a minimum. The result is an instrument with stray light below 5 millionths the brightness of the sun 50 arc-seconds from the sun. The COSMO-LC has just had a Preliminary Design Review (PDR) and the PDR design is presented.
We present an overview of the Off-plane Grating Rocket for Extended Source Spectroscopy (OGRESS)
sounding rocket payload based at the University of Iowa. OGRESS is designed to perform moderate resolution (R~10-
40) spectroscopy of diffuse celestial X-ray sources between 0.3 – 1.2 keV. A wire grid focuser constrains light from
diffuse sources into a converging beam that feeds an array of diffraction gratings in the extreme off-plane mount. The
spectrum is focused onto Gaseous Electron Multiplier (GEM) detectors. Scheduled to launch in 2014, OGRESS will
obtain accurate physical diagnostics of the Cygnus Loop supernova remnant and will increase the technical readiness
level of GEMs. OGRESS is the fourth-generation of similar payloads from the partnership between the University of
Iowa and the University of Colorado, with higher throughput, and improved noise characteristics over its predecessors.
The Micro-X High Resolution Microcalorimeter X-ray Imaging Rocket is a sounding rocket experiment
that will
combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to
obtain high- spectral-resolution images of extended X-ray sources. The target for Micro-X’s first
flight (slated for January
2013) is the Puppis A supernova remnant. The Micro-X observation of the bright eastern knot of
Puppis A will obtain a line-dominated spectrum with up to 27,000 counts collected in 300 seconds at
2 eV resolution across the 0.3-2.5 keV band. Micro-X will determine the thermodynamic and
ionization state of the plasma, search for line shifts and broadening associated with dynamical
processes, and seek evidence of ejecta enhancement. We describe the progress made in developing
this payload, including the detector, cryogenics, and electronics
assemblies.
We present results from the Extended X-ray Off-Plane Spectrometer (EXOS) sounding rocket payload. The
payload was launched on November 13, 2009 and successfully obtained a spectrum of the Cygnus Loop Supernova
Remnant. The instrument observed in the ~20 - 110 Angstrom bandpass with high resolution (~50) by utilizing an offplane
reflection grating array. This payload is also the 2nd flight for a relatively new type of detector, the Gaseous
Electron Multiplier (GEM) detector. We discuss the performance of these technologies in flight, as well as an overview
of our plans for the next flight of this design.
We present an overview of the Extended X-ray Off-Plane Spectrometer (EXOS) Sounding Rocket Payload
based at the University of Colorado, Boulder. The program includes a total of four launches over the next four years on
various x-ray sources. The payload utilizes off-plane reflection gratings and Gaseous Electron Multiplier (GEM)
detectors in order to achieve both high throughput and resolution (R~100).
A dispersive spectrometer onboard the International X-ray Observatory (IXO) provides a method for high throughput and
high spectral resolution at X-ray energies below 1 keV. An off-plane reflection grating array maximizes these
capabilities. We present here a mature mechanical design that places the grating array on the spacecraft avionics bus
13.5 m away from the focal plane. In addition, we present the technology development plan for advancing the
Technology Readiness Level to 6 for the Off-Plane X-ray Grating Spectrometer.
We present the results of the Astrophysics Strategic Mission Concept Study for the New Worlds Observer (NWO). We show that the
use of starshades is the most effective and affordable path to mapping and understanding our neighboring planetary systems, to opening
the search for life outside our solar system, while serving the needs of the greater astronomy community. A starshade-based mission
can be implemented immediately with a near term program of technology demonstration.
A dispersive spectrometer onboard the International X-ray Observatory (IXO) provides a method for high throughput and
high spectral resolution at X-ray energies below 1 keV. An off-plane reflection grating array maximizes these
capabilities. We present here a mature mechanical design that places the grating array on the spacecraft avionics bus
13.5 m away from the focal plane.
As currently envisioned, New Worlds Observer is a NASA flagship class mission, designed to fulfill the
Terrestrial Planet Finding mission objectives with a much more flexible architecture than the current TPF
design concepts. In this paper, we discuss the scalability of NWO for a variety of telescope sizes and briefly
discuss the associated science capability. In particular, the paper will address in detail three mission categories:
medium, large, and future mission concepts. Medium missions are missions with life cycle costs under $600
million dollars, including a version of NWO that may potentially fit within a MIDEX budget. Large missions
are flagship missions that involve significant science returns on a Observatory class level; this is our current
realization of NWO for the TPF mission. Future concepts use the NWO architecture, in conjunction with
enabling technologies such as in-space servicing, to solve long-term NASA missions such as Lifefinder and
Planet Imager. We present a multi-starshade NWO architecture designed for launch on an Ares V launch
vehicle as an example of a future concept.
Perhaps the most compelling piece of science and exploration now under discussion for future space missions is the
direct study of planets circling other stars. Indirect means have established planets as common in the universe but have
given us a limited view of their actual characteristics. Direct observation holds the potential to map entire planetary
systems, view newly forming planets, find Earth-like planets and perform photometry to search for major surface
features. Direct observations will also enable spectroscopy of exoplanets and the search for evidence of simple life in
the universe. Recent advances in the design of external occulters - starshades that block the light from the star while
passing exoplanet light - have lowered their cost and improved their performance to the point where we can now
envision a New Worlds Observer that is both buildable and affordable with today's technology. In this paper we explore
the comparison of scientific capability of external occulters relative to indirect means and to internal coronagraph
missions. We conclude that external occulters logically provide the architecture for the next space mission for exoplanet
studies.
The orbital light curve of a terrestrial exoplanet will likely contain valuable information about the surface and
atmospheric features of the planet, both in its overall shape and hourly variations. We have constructed an empirically
based code capable of simulating observations with a New Worlds Observatory of Earth from any orientation, at any
time of year with continuously updated cloud and terrain coverage. By simulating these observations over a full orbital
revolution we determine that the detection of liquid surface water is possible during crescent phases of planetary systems
at high inclinations, while the detection of an obliquity / seasonal terrain change is possible at low inclinations. A New
Worlds Observer can accurately determine the rotation rate of the planet more than 50% of the time given only 5 days of
observations with a S/N of ~10.
We present laboratory studies of scaled occulting starshades for the New Worlds Observer (NWO). A deep
reactive ion etched silicon starshade has been fabricated by NIST, designed to cover the same number of Fresnel zones
as in the proposed mission. The broadband shadow is mapped with a photometer in a dark vacuum tunnel fed by a
heliostat at HAO. CCD images provide direct contrast measurements of different features around the starshade.
Preliminary measurements reach 5x10-6 suppression in the center of the shadow at the focal plane. The two-dimensional
structure of the starshade diffraction pattern is compared to that produced by the Fresnel integral.
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